DESCRIPTION: The purpose of this project is to describe the encoding of speech sound differences in the human cerebral cortex, specifically, the nature of early acoustic-phonetic analyses that map acoustic cues onto abstract phonetic representations of speech sounds. The methodology involves coupling behavioral testing with two well-established clinical techniques: direct cortical electrical interference and intracarotid sodium amobarbital testing. Preliminary studies confirmed the efficacy of this approach, established a critical role for cortical processing in speech discrimination, and provided the foundation for three working hypotheses: (1) Cortical encoding is differentially sensitive to consonant-vowel, but not to traditional consonant feature differences; (2) Acoustic-phonetic analyses for speech discrimination are also required for auditory access to lexical processing; and (3) Cortical regions critical for speech discrimination are highly localized with lateral left perisylvian cortex. The proposed studies will assist in determining the scope of cortical sensitivity to acoustic-phonetic information and in identifying critical underlying neuroanatomic structures.